If you can answer the following questions in order, then I think you'll arrive at the solution:

1.) What is the potential energy at moment A?
2.) What is the kinetic energy at moment A?
3.) What is the total energy at moment A?
4.) What therefore must be the total energy at any moment?
5.) What is the potential energy at moment B? (You already got this one).
6.) Using your answers to questions 4 and 5, what is the kinetic energy at moment B?